The Traceable Event Dispatcher

The TraceableEventDispatcher
is an event dispatcher that wraps any other event dispatcher and can then
be used to determine which event listeners have been called by the dispatcher.
Pass the event dispatcher to be wrapped and an instance of the
Stopwatch to its constructor:

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useSymfony\Component\EventDispatcher\Debug\TraceableEventDispatcher;useSymfony\Component\Stopwatch\Stopwatch;// the event dispatcher to debug$dispatcher=...;$traceableEventDispatcher=newTraceableEventDispatcher($dispatcher,newStopwatch());

Now, the TraceableEventDispatcher can be used like any other event dispatcher
to register event listeners and dispatch events:

After your application has been processed, you can use the
getCalledListeners()
method to retrieve an array of event listeners that have been called in
your application. Similarly, the
getNotCalledListeners()
method returns an array of event listeners that have not been called: